We shall explore the differentiation and interaction of effector T-lymphocytes using somatic cell genetic techniques. Three interdependent problems will be undertaken. First, we are continuing our analysis of the antigenic properties and biological behavior of Thy-1 variants of the BALB/c T-cell lymphoma, RL01, and other T-cell derived tumors. Second, we plan to expand these studies to other surface markers found on T-cells and T-cell tumors and, finally, we plan to extend this to the study of immunoselected variants of cloned lines of normal murine T-cells.